Postharvest Physiological Deterioration Research Articles

Systematic Analysis of Cinnamyl Alcohol Dehydrogenase Family in Cassava and Validation of MeCAD13 and MeCAD28 in Lignin Synthesis and Postharvest Physiological Deterioration.

Cassava (Manihot esculenta Crantz) is used as a biomass energy material and an effective supplement for food and feed. Cinnamyl alcohol dehydrogenase (CAD) catalyzes the final step of lignin biosynthesis and is responsible for various stresses. However, systematic investigations of the CAD gene family in cassava have been poorly understood. In this study, a genome-wide survey and bioinformatics analysis of CAD gene family was performed, transcriptomics, qRT-PCR, gene silencing and stress of yeast cell were used for excavate and validate the candidate MeCADs gene. 36 MeCADs genes unevenly distributed across 12 chromosomes were identified. Through phylogenetic analyses alongside their Arabidopsis counterparts, these MeCADs were divided into four groups, each containing a similar structure and conserved motifs. Interestingly, transcriptome data analysis revealed that 32 MeCAD genes were involved in the postharvest physiological deterioration (PPD) process, whereas 27 MeCAD genes showed significant changes. Additionally, the relative quantitative analysis of 6 MeCAD genes demonstrated that they were sensitive to PPD, suggesting that they may be involved in the regulation of PPD. Silencing MeCAD13 and MeCAD28 further showed that lignin content significantly decreased in the leaves. The wound-stress tolerance of transgenic yeast cells was enhanced after transformation with MeCAD13 and MeCAD28. MeCAD13 and MeCAD28 may play positive roles in lignin biosynthesis and PPD response, respectively. These results provided a systematic functional analysis of MeCADs in cassava and paved a new way to genetically modify lignin biosynthesis and PPD tolerance.

Physiological and Microstructure Analysis Reveals the Mechanism by Which Formic Acid Delays Postharvest Physiological Deterioration of Cassava.

Formic acid is reported to act as a food preservative and feed additive, but its effects on controlling postharvest physiological deterioration (PPD) development in cassava are unclear. In this study, we assessed the effectiveness of different concentrations of formic acid in attenuating PPD occurrence in fresh-cut cassava. The results showed that the concentration of 0.1% (v/v) formic acid could significantly delay the occurrence of PPD, and that the higher the concentration of formic acid supplied, the later the occurrence of PPD symptoms. The physiological and biochemical analysis of 0.5%-formic-acid-treated cassava slices revealed that formic acid decreased the degradation of starch, inhibited the accumulation of hydrogen peroxide (H2O2), malondialdehyde (MDA), and water-soluble pectin in cassava slices with PPD development, and increased the activities of the antioxidant enzymes ascorbate peroxidase (APX) and glutathione reductase (GR). A microscopic observation showed that the formic acid treatment inhibited the enlargement of the intercellular space during the cassava PPD process, which suggests that the formation of an intercellular layer of the cell wall was inhibited by formic acid. This study thus revealed the mechanism used by formic acid to extend the cassava shelf life; however, a detailed evaluation of the possible side effects on, for example, the cyanide content will be needed to categorically ensure the safety of this method.

Effect of packaging and storage conditions on the pasting and functional properties of pretreated yellow-fleshed cassava flour

Cassava is highly susceptible to post harvest physiological deterioration which makes it necessary to initiate processing so as to extend the shelf life. In order to improve and enhance the nutritional characteristics of the processed cassava flour, this research was carried out so as to evaluate the adequate packaging materials and storage conditions necessary for safe storage and good flour quality. Pasting properties of food/flour is an indication of the different applicability of starch-based food ingredients in product development. The effect of packaging materials (cylindric polyvinyl containers and aluminum ziplock pouch bags) on quality attributes of pretreated yellow-fleshed cassava flour (YFCF) samples stored in two storage conditions a (cooling chamber at 5 °C and 30 % relative humidity and; in a climate chamber at 30 °C and 50 % relative humidity) was investigated for 8 weeks. Flour samples from each package type were evaluated for water absorption capacity, pasting and oil absorption capacity fortnightly. The treated initial flour sample before storage-sulfured (BSS) had the highest peak viscosity (891 RVU). The low peak time at the end of storage in non-sulfured flours packed in aluminum pouch bags and stored at 5 °C is an evidence of time and energy saving capacity. The water absorption capacity of non-sulfured flour samples packed in cylindric polyvinyl containers and the sulfured flour sample packed in an aluminum pouch bag at 30 °C increased with storage duration. The aluminum ziplock pouch bags showed excellent storage quality and retained better pasting property. The climatic storage condition revealed better keeping quality. The use of sodium metabisulphite revealed its suitability as a pretreatment tool.

Proline inhibits postharvest physiological deterioration of cassava by improving antioxidant capacity

Cassava (Manihot esculenta Crantz), a crucial global tuber crop, encounters significant economic losses attributed to postharvest physiological deterioration (PPD). The PPD phenomenon in cassava is closely related to the accumulation of reactive oxygen species (ROS), and amino acids play a pivotal role in regulating signaling pathways and eliminating ROS. In this study, the storage performance of eight cassava varieties were conducted. Cassava cultivar SC5 showed the best storage performance among the eight cassava varieties, but the edible cassava cultivar SC9 performed much worse. Comparative analysis of free amino acids was conducted in eight cassava varieties, revealing changes in proline, aspartic acid, histidine, glutamic acid, threonine, and serine. Exogenous supplementation of these six amino acids was performed to inhibit PPD of SC9. Proline was confirmed as the key amino acid for inhibiting PPD. Treatment with optimal exogenous proline of 5 g/L resulted in a 17.9% decrease in the deterioration rate compared to untreated cassava. Accompanied by a decrease in H2O2 content and an increase in catalase, superoxide dismutase and ascorbate peroxidase activity. Proline treatment proved to be an effective approach to alleviate cell oxidative damage, inhibit PPD in cassava, and prolong shelf life.

Elucidating the molecular mechanisms in phytohormones-induced alleviation of postharvest physiological deterioration in cassava tuberous roots

Cassava is a staple food crop in tropical regions, serving as a significant source of carbohydrates. However, rapid postharvest physiological deterioration (PPD) significantly limits the shelf life and utilization of cassava. Despite its importance, the overlapping molecular mechanisms underlying phytohormones-induced PPD alleviation in cassava tuberous roots remain unknown. In this study, the phytohormones ethephon (ET), gibberellic acid (GA), and methyl jasmonate (MeJA) were applied to cassava tuberous roots after harvest. These treatments led to significantly reduced H2O2 accumulation and alleviation of PPD. Transcriptomic analysis revealed shared functions, including transcriptional regulation and oxidoreductase activity, among differentially expressed genes (DEGs) affected by ET, GA, or MeJA. A total of 305 genes encoding antioxidant enzymes were systematically identified, with 151 responsive to phytohormone treatments across ten families. Notably, the expression of 10 Glutathione S-transferase (GST) genes was induced by all three phytohormone treatments, while their expression was suppressed in the absence of phytohormones during PPD. By using co-expression network analysis, DNA-binding motif analysis, and experimental validation using yeast one-hybrid and dual-luciferase assays, a regulatory network involving MeMYB102 and MeZAT11 transcription factors (TFs) that directly promote the expression of MeGST42, MeGST43, MeGST44, and MeGST46 was established. Overall, this study enhances the understanding of the overlapping molecular mechanisms underlying phytohormones-induced alleviation of PPD in cassava, thereby providing genetic resources for developing PPD-resistant cassava.

Biochemical characterisation of a cassava (Manihot esculenta crantz) diversity panel for post-harvest physiological deterioration; metabolite involvement and environmental influence

Cassava (Manihot esculenta Crantz) produces edible roots, a major carbohydrate source feeding more than 800 million people in Africa, Latin America, Oceania and Asia. Post-harvest physiological deterioration (PPD) renders harvested cassava roots unpalatable and unmarketable. Decades of research on PPD have elucidated several genetic, enzymatic and metabolic processes involved. Breeding populations were established to enable verification of robust biomarkers for PPD resistance. For comparison, these PPD populations have been cultivated concurrently with diversity population for carotenoid (β-carotene) content. Results highlighted a significant variation of the chemotypes due to environmental factors. Less than 3% of the detected molecular features showed consistent trends between the two harvest years and were putatively identified as phenylpropanoid derived compounds (e.g. caffeoyl rutinoside). The data corroborated that ∼20 μg β-carotene/g DW can reduced the PPD response of the cassava roots to a score of ∼1. Correlation analysis showed a significant correlation of β-carotene content at harvest to PPD response (R2 -0.55). However, the decrease of β-carotene over storage was not significantly correlated to initial content or PPD response. Volatile analysis observed changes of apocarotenoids derived from β-carotene, lipid oxidation products (alkanes, alcohols and carbonyls and esters) and terpenes. The majority of these volatiles (>90%) showed no significant correlation to β-carotene or PPD. Observed data indicated an increase (∼2-fold) of alkanes in varieties with β-carotene >10 μg/g DW and a decrease (∼60%) in varieties with less β-carotene. Fatty acid methyl esters with a chain length > C9 were detected solely after storage and show lower levels in varieties with higher β-carotene content. In combination with correlation values to PPD (R2 ∼0.3; P-value >0.05), the data indicated a more efficient ROS quenching mechanism in PPD resistant varieties.

RNA splicing modulates the postharvest physiological deterioration of cassava storage root.

Rapid postharvest physiological deterioration (PPD) of cassava (Manihot esculenta Crantz) storage roots is a major constraint that limits the potential of this plant as a food and industrial crop. Extensive studies have been performed to explore the regulatory mechanisms underlying the PPD processes in cassava to understand their molecular and physiological responses. However, the exceptional functional versatility of alternative splicing (AS) remains to be explored during the PPD process in cassava. Here, we identified several aberrantly spliced genes during the early PPD stage. An in-depth analysis of AS revealed that the abscisic acid (ABA) biosynthesis pathway might serve as an additional molecular layer in attenuating the onset of PPD. Exogenous ABA application alleviated PPD symptoms through maintaining ROS generation and scavenging. Interestingly, the intron retention transcript of MeABA1 (ABA DEFICIENT 1) was highly correlated with PPD symptoms in cassava storage roots. RNA yeast 3-hybrid and RNA immunoprecipitation (RIP) assays showed that the serine/arginine-rich protein MeSCL33 (SC35-like splicing factor 33) binds to the precursor mRNA of MeABA1. Importantly, overexpressing MeSCL33 in cassava conferred improved PPD resistance by manipulating the AS and expression levels of MeABA1 and then modulating the endogenous ABA levels in cassava storage roots. Our results uncovered the pivotal role of the ABA biosynthesis pathway and RNA splicing in regulating cassava PPD resistance and proposed the essential roles of MeSCL33 for conferring PPD resistance, broadening our understanding of SR proteins in cassava development and stress responses.

Assessment of Yellow and White Fleshed Cassava Tuberous Root Cultivars Reveals Different Responses to Post-harvest Physiological Deterioration

Identification of post-harvest physiological deterioration (PPD) tolerance in cassava is crucial, as PPD significantly hampers the cassava tuberous root industry by shortening storage periods post-harvest and diminishing product quality. Characteristics linked to PPD tolerance encompass high carotenoid levels and low dry matter content (DMC). This study aimed to evaluate the PPD responses of six yellow fleshed and ten white-fleshed cassava tuberous roots and determine the source of PPD tolerance. PPD and DMC assessments were conducted using standard methods at three storage periods: 2, 5, and 10 days after harvest (DAH). The k-means clustering analysis revealed six clusters, each corresponding to distinct PPD symptom patterns and tolerance statuses. Cluster 1, comprising three yellow-fleshed and three white-fleshed cassava cultivars, demonstrated PPD tolerance with minimal symptoms up to 5 DAH. Clusters 2 and 3 exhibited a moderate PPD response with elevated symptoms at 5 DAH, comprising three yellow-fleshed and three white-fleshed cassava cultivars. Clusters 4 to 6 displayed a sensitive response to PPD, showcasing a significant increase in symptoms at 5 and 10 DAH, with four white-fleshed cassava cultivars identified within this cluster. These findings underscored the presence of PPD tolerance in both yellow-fleshed and white-fleshed cassava tuberous roots. The correlation between PPD and DMC was significant only at 2 DAH, displaying a moderate positive correlation. Consequently, this study identified three cultivars, “Carvita-25”, “Manggu”, and ““Ubi Kuning””, with high DMC and low PPD incidence at 5 DAH, suggesting their suitability for further breeding programs.

CRISPR-Cas9-induced targeted mutagenesis of feruloyl CoA 6′-hydroxylase gene reduces postharvest physiological deterioration in cassava roots

Cassava is a starch-rich, multipurpose root crop grown by millions of smallholder farmers in tropical and subtropical countries. Cassava cultivation is seriously constrained by post-harvest physiological deterioration (PPD) of roots that occurs within 24–72 h after harvest, making them unpalatable and unmarketable. The inevitable wounding of roots during harvest triggers an oxidative burst throughout the root together with the accumulation of secondary metabolites with scopoletin being the most abundant. Blue-black discoloration and vascular streaking observed during PPD occur due to over-accumulation of scopoletin whose biosynthesis involves key enzymes including feruloyl CoA 6′-hydroxylase.We applied the CRISPR-Cas9 system for targeted mutagenesis of feruloyl CoA 6′-hydroxylase genes (MeF6'H1, MeF6'H12 MeF6'H2 and MeF6'H3) in cassava to delay PPD. To generate cassava plants with enhanced root shelf-life, CRISPR-Cas9 cassettes with Cas9 gene and sgRNA targeting three genes; MeF6'H1, MeF6'H2, and MeF6'H3 were introduced into cassava via Agrobacterium-mediated transformation. Integration of transgenes in putative knockout plants were confirmed by PCR while targeted sanger sequencing revealed CRISPR-Cas9 induced mutations with insertion, deletions and substitution being reported upstream and downstream of the PAM sequence of target genes. Targeted for edition of dual genes exhibited significant reduction of scopoletin below HPLC detectable levels and had improved shelf-life compared to one gene knockout events and wild-type plants. Evaluation of phenotypic variations between mutant and wild-type cassava plants revealed mutation-event associated traits including stem and petiole depigmentation, auxiliary budding, claw-like leaf appearance, loss of apical dominance and leaf chlorosis. This study demonstrated an effective and feasible approach to extend cassava root shelf-life to stabilize yield production, prevent postharvest wastage, and improve farmers’ income.

MePOD12 participates the regulation to postharvest physiological deterioration by ROS scavenging and lignin accumulation in cassava tuberous roots

Cassava tuberous root, as a staple food crop and industrial raw material worldwide, is highly sensitive to postharvest physiological deterioration (PPD) caused by wound. However, the molecular mechanism underlying PPD tolerance remains elusive in cassava. The reactive oxygen species (ROS) scavenging system is activated at the preliminary stage of PPD and peroxidase (POD) can effectively eliminate ROS. The expression level of MePOD12 and POD enzymatic activity in cassava tuberous roots was considerably up-regulated with PPD occurrence. Yeast two-hybrid and luciferase reporter assay showed that MePOD12 physically interacted with lignin-related cinnamyl alcohol dehydrogenase 15 (MeCAD15) in vitro and in vivo. The MePOD12-silenced tuberous roots decayed more than control, especially stored at room temperature for 3 and 5 days after harvesting. The total antioxidant capacity, activities of POD, SOD, CAT, CAD and lignin content were lower than those of control. Particularly, after harvest for 3 days, the accumulation of hydrogen peroxide and superoxide anion substantially increased compared to control. In addition, a proposed model was generated to elaborate the response mechanism of MePOD12 participating in PPD regulation via ROS elimination and lignin accumulation. It provides a new clue for breeding cassava PPD-tolerant varieties.

The Genome-Wide Identification of Stable Internal Reference Genes Related to Delayed Spoilage for Accurate qRT-PCR Normalization in Ethephon-Treated Pueraria thomsonii Benth.

Pueraria thomsonii Benth. is a perennial leguminous vine with medicinal and nutritional value. However, rapid postharvest physiological deterioration (PPD) reduces its quality and market value. To detect gene expression levels, the quantitative reverse transcription polymerase chain reaction (qRT-PCR) technique requires stable internal reference genes (IRGs). Our findings indicated that an ethephon (C2H6ClO3P) treatment delayed PPD in P. thomsonii tuberous roots and an RNA-seq analysis revealed a significant number of differentially expressed genes (DEGs). To find stable IRGs for the further identification of the genes associated with delayed PPD in P. thomsonii, eight candidate IRGs of the tuberous roots were screened and assessed using qRT-PCR. The expression stability of these genes was determined and ranked using five different algorithms, including NormFinder, BestKeeper, ΔCt, GeNorm, and ReFinder. Consequently, we identified two genes, PtUBC10 and PtACT7, as the best candidate IRGs for qRT-PCR normalization in P. thomsonii, both exposed to ethephon treatment and in different tissues. Moreover, PtUBC10 was found to be the most stably expressed IRG of P. thomsonii during the ethephon treatment. The findings of this investigation furnish significant insights for future gene expression analyses concerning the delay of PPD via ethephon administration, which could also be used in other tuberous plants.

Varietal screening for identification of postharvest physiological deterioration tolerance in storage roots of cassava

ABSTRACT Postharvest physiological deterioration (PPD) is a constraint in cassava (Manihot esculenta Crantz) and a threat to effective utilization of cassava roots. This study determined the magnitude of variability for PPD tolerance among cassava genotypes and identified new sources of tolerance to PPD. Seventy-six cassava genotypes were evaluated for PPD tolerance at postharvest evaluation intervals of 3, 5, 7, 10, 15, or 20 days after harvest. Repeated measure analysis indicated that differences for PPD reliably depend on time in conjunction with genotype and years. The genotypes were categorized into nine classes using rank-sum statistics involving standardized mean range, PPD, and PPD per day. Nineteen genotypes were tolerant and three were free of symptoms up to 20 days postharvest. Released varieties had tolerance to PPD compared to local varieties and pre-breeding lines. The PPD symptoms were mostly found in peripheral regions and in proximal and distal ends rather than in the mid-region of the root. The presence of the root neck reduced deterioration. Root length, weight, and dry matter content were positively correlated with PPD. The new sources of tolerance may improve the adoption and utilization of cassava.

Metabolite fingerprinting of cassava (Manihot esculenta Crantz) landraces assessed for post-harvest physiological deterioration (PPD).

Cassava landraces are impacted by post-harvest physiological deterioration (PPD). 34 primary/secondary metabolites (carotenes, flavonols, indols, phenolic, hydroxycinnamic, and organic acids) were analysed using HPLC/GC-MS in 72 landraces harvested 8months after planting (MAP) to clarify whether these compounds may play a role in PPD tolerance. Cluster analysis differentiated a first group with high organic acids contents, citric acid being dominant, a second group with landraces high in tryptophan, a third group including landraces with high phenolic and hydroxycinnamic acids content, and a fourth group characterised by 8 carotenoids. PPD tolerant and susceptible landraces were present in each group. To determine if PPD is related to age of harvest, 174 landraces were harvested at 6, 8, 10 and 12 MAP. Scopoletin, sucrose and glucose were analysed. PPD was positively correlated with DMC and negatively correlated with scopoletin at all ages of harvest. Scopoletin is a useful biomarker to characterize landraces.

Integrated Characterization of Cassava (Manihot esculenta) Pectin Methylesterase (MePME) Genes to Filter Candidate Gene Responses to Multiple Abiotic Stresses.

Plant pectin methylesterases (PMEs) play crucial roles in regulating cell wall modification and response to various stresses. Members of the PME family have been found in several crops, but there is a lack of research into their presence in cassava (Manihot esculent), which is an important crop for world food security. In this research, 89 MePME genes were identified in cassava that were separated into two types (type-Ⅰ and type-Ⅱ) according to the existence or absence of a pro-region (PMEI domain). The MePME gene members were unevenly located on 17 chromosomes, with 19 gene pairs being identified that most likely arose via duplication events. The MePMEs could be divided into ten sub-groups in type-Ⅰ and five sub-groups in type-Ⅱ. The motif analysis revealed 11 conserved motifs in type-Ⅰ and 8 in type-Ⅱ MePMEs. The number of introns in the CDS region of type-Ⅰ MePMEs ranged between one and two, and the number of introns in type-Ⅱ MePMEs ranged between one and nine. There were 21 type-Ⅰ and 31 type-Ⅱ MePMEs that contained signal peptides. Most of the type-Ⅰ MePMEs had two conserved "RK/RLL" and one "FPSWVS" domain between the pro-region and the PME domain. Multiple stress-, hormone- and tissue-specific-related cis-acting regulatory elements were identified in the promoter regions of MePME genes. A total of five co-expressed genes (MePME1, MePME2, MePME27, MePME65 and MePME82) were filtered from different abiotic stresses via the use of UpSet Venn diagrams. The gene expression pattern analysis revealed that the expression of MePME1 was positively correlated with the degree of cassava postharvest physiological deterioration (PPD). The expression of this gene was also significantly upregulated by 7% PEG and 14 °C low-temperature stress, but slightly downregulated by ABA treatment. The tissue-specific expression analysis revealed that MePME1 and MePME65 generally displayed higher expression levels in most tissues than the other co-expressed genes. In this study, we obtain an in-depth understanding of the cassava PME gene family, suggesting that MePME1 could be a candidate gene associated with multiple abiotic tolerance.

Genome-wide analysis of the metallothionein gene family in cassava reveals its role in response to physiological stress through the regulation of reactive oxygen species

BackgroundCassava (Manihot esculenta Crantz) is widely planted in tropical and several subtropical regions in which drought, high temperatures, and other abiotic stresses occur. Metallothionein (MT) is a group of conjugated proteins with small molecular weight and rich in cysteine. These proteins play a substantial role in response to physiological stress through the regulation of reactive oxygen species (ROS). However, the biological functions of MT genes in cassava are unknown.ResultsA total of 10 MeMT genes were identified in the cassava genome. The MeMTs were divided into 3 groups (Types 2–4) based on the contents and distribution of Cys residues. The MeMTs exhibited tissue-specific expression and located on 7 chromosomes. The MeMT promoters contain some hormones regulatory and stresses responsiveness elements. MeMTs were upregulated under hydrogen peroxide (H2O2) treatment and in respond to post-harvest physiological deterioration (PPD). The results were consistent with defense-responsive cis-acting elements in the MeMT promoters. Further, four of MeMTs were selected and silenced by using the virus-induced gene silencing (VIGS) method to evaluate their functional characterization. The results of gene-silenced cassava suggest that MeMTs are involved in oxidative stress resistance, as ROS scavengers.ConclusionWe identified the 10 MeMT genes, and explore their evolutionary relationship, conserved motif, and tissue-specific expression. The expression profiles of MeMTs under three kinds of abiotic stresses (wounding, low-temperature, and H2O2) and during PPD were analyzed. The tissue-specific expression and the response to abiotic stresses revealed the role of MT in plant growth and development. Furthermore, silenced expression of MeMTs in cassava leaves decreased its tolerance to ROS, consistent with its predicted role as ROS scavengers. In summary, our results suggest an important role of MeMTs in response to physiological stress as well as species adaptation via the regulation of ROS homeostasis.

Reactive oxygen species turnover, phenolics metabolism, and some key gene expressions modulate postharvest physiological deterioration in cassava tubers.

Rapid postharvest physiological deterioration (PPD) in cassava (Manihot esculenta Crantz) tuber is a significant concern during storage. The freshly harvested tubers start spoiling within 24 to 72 h. Accumulation of H2O2 is one of the earliest biochemical events that occurred during PPD, which was detected using the 3,3 diaminobenzidine (DAB) in two contrast cassava genotypes, MNP Local A (29-57 μg g-1) and Sree Prakash (64-141 μg g-1). Accumulating the fluorescence hydroxycoumarin compounds emitted by the cassava tubers observed under an ultraviolet (UV) lamp showed significant variations at 0, 3, 6, 9, 12, and 15 days of storage. The total phenolics and carotenoids significantly and negatively correlated with PPD progression; however, the anthocyanin and flavonoids positively correlated with the PPD-anchored ROS accumulation. The primary compound, Phthalic acid, di(2-propylpentyl) ester, was identified in both the cassava tubers, Sree Prakash (57.21 and 35.21%), and MNP Local A (75.58 and 60.21%) at 0, and 72 h of PPD, respectively. The expression of PPD-associated genes APX-2, APX-3, PAL, and AP was higher at 6-12 days of PPD, which signified the synthesis of ROS turnover and phenylpropanoid biosynthesis. A significant, strong, and positive correlation was established between the secondary metabolites and PPD signaling gene expression, which was inversely correlated with hydroxycoumarin and H2O2 accumulation. MNP Local A tubers exhibited longer storage life of 15 days with a low PPD score, higher metabolites synthesis, and gene expression. The PPD-resistant lines may be used to augment cassava breeding strategies for large-scale commercial and industrial use.

In-vitro effects of sucrose and ascorbic acid on induction and shelf-life of micro-tuber of cassava (Manihot esculenta Crantz) genotypes

Background: Cassava production faces threat from postharvest physiological deterioration (PPD). The PPD is usually observed within the first 72 hours of harvest. Therefore, extending the shelf-life of cassava root-tubers by few days could reduce appreciable financial losses. Objective: This study is aimed to investigate effects of sucrose and ascorbic acid on induction and shelf-life of micro-tubers of cassava cultivars using an In-vitro model. Method: Effect of sucrose (30, 45, 60, 75 and 90 g/L) on the micro-tuber induction was determined after 45 days in these cultivars (TME 1333 and TME 2060). The optimal level was later combined with ascorbic acid (0, 25, 50, 75 and 100 mg/L) to investigate its effect on micro-tubers shelf-life during a 10-day storage. Each study was laid out in factorial under CRD with 5 replications. Results: The 30 g/L sucrose (control) produced the utmost number of micro-tubers (4.33), highest length (6.68 cm), and fresh weight (0.1495 g). The cultivar ‘TME 2060’ had longer (5.26 cm) and higher fresh weight (0.1079 g) than ‘TME 1333’ with 5.04 cm and 0.0977 g respectively. Ascorbic acid (100 mg/L) significantly delayed the discolouration of micro-tubers over a 10-day storage. Also, the 100 mg/L ascorbic acid produced the least percentage of deteriorated micro-tubers. Conclusion: Results demonstrate the roles of sucrose and ascorbic acid in micro-tuber formation and antioxidant activity in delaying PPD. Therefore, we propose for In-situ production (via breeding strategy) of vitamin C-fortified cassava varieties in order to control the incidence of PPD and in turn improve farmer`s economy.

A method for rapid and homogenous initiation of post-harvest physiological deterioration in cassava storage roots identifies Indonesian cultivars with improved shelf-life performance

Cassava is the most cultivated and consumed root crop in the world. One of the major constraints to the cassava value chain is the short shelf life of cassava storage roots which is primarily due to the so-called post-harvest physiological deterioration (PPD). The identification of natural sources of PPD tolerance represents a key approach to mitigating PPD losses by generating farmer- and industry-preferred cassava cultivars with prolonged shelf life. In the present study, a PPD assessment method was developed to screen for PPD tolerance in the cassava germplasm. The proposed PPD assessment method displayed a reduced rate of microbial infection and allowed a rapid and homogenous development of typical PPD symptoms in the cassava storage roots. We successfully used the PPD assessment method in combination with an image-based PPD scoring method to identify and characterize PPD tolerance in 28 cassava cultivars from the Indonesian cassava germplasm. Our analysis showed a significant and positive correlation between PPD score and dry matter content (r = 0.589–0.664, p-value < 0.001). Analysis of additional root parameters showed a significant and positive correlation between PPD scores at 2 days post-harvest (dph) and root length (r = 0.388, p-value < 0.05). Our analysis identified at least 4 cultivars displaying a significantly delayed onset of PPD symptoms as compared to the other selected cultivars. The availability of cassava cultivars contrasting for tolerance to PPD will be particularly instrumental to understanding the molecular mechanisms associated with delayed PPD in cassava roots.

Flavonoid accumulation modulates the responses of cassava tuberous roots to postharvest physiological deterioration

Postharvest physiological deterioration (PPD) caused by wounding is one of the main constraints that affect the development of cassava industry. However, the molecular mechanisms underlying the PPD are unknown. In the present study the adaptive response to wound stress was analyzed in combination with transcriptome and metabolome in four kinds of PPD phenomenon from cassava tuberous roots. The results indicated that starch, β-carotene, (-)-epigallocatechin, cyanidin-3-O-glucoside, and L-epicatechin were altered in the wounded tuberous roots. Moreover, the ROS scavenging system was activated at the PPD preliminary stage. Transcriptome analysis further showed that the strongly induced genes were mainly related to carbohydrate metabolism, signal transduction, and polyketide metabolism. Twenty-eight differentially expressed genes (DEGs) in the flavonoid pathway were preferably enriched. The relative quantitative analysis of seventeen genes demonstrated that they were responsive to PPD. Fifty-one differential flavonoid metabolites were detected in widely targeted metabolome profile, among which, luteolin, kaempferol, (-) epicatechin, phloretin, and naringenin were enhanced during PPD. The virus-induced gene silencing of MeCHS3 and MeANR showed that tuberous roots changed tolerance to PPD, and the total flavonoid and anthocyanin contents in leaves were changed. Therefore, the candidate genes and metabolites in flavonoid pathways could participate in PPD regulation. In addition, a proposed model was generated to elaborate the response mechanism of flavonoids under wounding stress, thus providing a future direction for breeding PPD-tolerant cultivars of cassava.

Functional Compound Changes during Postharvest Physiological Deterioration of Cassava Tuber

Reducing the economic value of the cassava tuber crop, thereby Postharvest Physiological Deterioration (PPD) is the major problem in cassava that renders the tuber unmarketable. After harvest of cassava tuber causing fluorescence in the storage parenchyma was observed, because changes in metabolic compound mainly responsible for the fluorescence. Its content peaks within 24 hours of injury and prior to the development of the visual symptoms of physiological deterioration. The present study of Fourier infrared transform spectroscopy (FTIR) was performed with CI 850, YTP 1, H740/92 and H226 cassava genotypes to identify the functional compound changes during Postharvest Physiological Deterioration. FTIR spectroscopy is a technique based on the determination of the interaction between infrared (IR) radiation and a sample. The present study revealed that the extracts of fresh cassava tuber and stored tubers of different cassava genotypes, has potential to produce bioactive functional compounds like hydrocarbons, oxygen compounds, nitrogen containing compounds, isocyanates, thiocyanide, cyanide, isothiocyanates, oxidized nitrogen functions, sulfur compounds, phosphorous and amides but their quantity was differently in cassava genotypes which correlate with reinforcement of tolerance to PPD under storage condition.